Lubricating grease composition

ABSTRACT

Use of a lubricating grease composition-comprising: (A) base oil selected from mineral oil, synthetic oil or mixtures thereof; (B) one or more urea compounds; and (C) one or more metal salts of a fatty acid wherein the metal is selected from the group consisting of aluminium, magnesium, zinc, calcium and mixtures thereof, in order to reduce fretting corrosion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Japanese Patent Application No. 2004-364252, filed on Dec. 16, 2004, which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a lubricating grease composition with improved fretting characteristics.

Fretting corrosion in grease lubrication differs from general chemical corrosive abrasion. It is a species of the mechanical abrasion phenomenon. Various studies of lubricating agents have been made in order to constrain or prevent it.

BACKGROUND OF THE INVENTION

In general, the places where fretting corrosion is liable to occur are many and various. It occurs not only in the wheel bearing area in cars but also in various areas of machines where two bodies such as splines, couplings, leaf springs and bearings are in contact and are subject to minute vibrations or sliding relative to each other.

Fretting refers to the case where microvibrations or microscopic sliding occur between two bodies opposed to each other, and the abrasion dust generated by the microvibrations between steel and steel turns, in the atmosphere, into a fine, brown iron oxide powder which then mixes with the grease, so that the grease turns a brown colour. The abrasion generated by these relative microvibrations is called fretting or microvibration abrasion and, because it is accompanied by oxidation in the atmosphere, it may be called fretting corrosion.

SUMMARY OF THE INVENTION

Although fretting corrosion itself has a small detrimental effect directly on bearing performance, it is known to promote abrasion on the rolling-contact surfaces and raceway surfaces when abrasion dust enters the bearing and so to be a cause of noise.

Laid-open Japanese Patent Application 2003-231893 describes a grease composition which has excellent low-torque performance, anti-fretting performance and low out-gas performance, being a grease composition containing an alkali metal salt or an alkaline earth metal salt of a higher fatty acid as a thickening agent, two types of carbonic acid ester compounds having different kinematic viscosities, and a metal salt of an organic sulphonic acid where the metal salt is from an alkali metal, an alkaline earth metal or zinc.

Laid-open Japanese Patent Application 2002-265970 describes a grease composition capable of improving acoustic performance and anti-fretting performance of ball bearings simultaneously, being a grease composition comprised of a base oil and a thickening agent as the principal constituents, where the thickening agent is comprised of a mixture of a urea compound and a lithium soap.

EP-A-1314774 describes a lubricating grease composition for use in constant velocity joints (CVJs) which is said to have anti-flaking and anti-seizure properties.

Said lubricating grease composition comprises lubricant base oil, 0.01 to 10% by mass of a fatty acid salt, 0.01 to 10% by mass of carbonate; 2 to 30% by mass of a thickener; and 0.1 to 20% by mass of a sulphur type extreme-pressure agent.

EP-A-0767237 discloses a lubricating grease composition for a constant velocity joint containing a base oil, a thickener, boron nitride powders, and a sulphur-phosphorus containing extreme pressure agent.

EP-A-0767237 states that said lubricating grease composition exhibits superior anti-flaking performance and can prolong the lifetime of a constant velocity joint.

It is indicated in EP-A-0767237 that said lubricating grease composition may further comprise an organic compound such as zinc dithiophosphate, zinc salts of fatty acids and zinc naphthenate, in order to further improve the anti-flaking performance.

EP-A-0761806 describes a lubricating grease composition comprising a major amount of an oil of lubricating viscosity, a thickener selected from the group consisting of monoureas, diureas, triureas and polyureas, or mixtures thereof, and an oil soluble neutral or overbased zinc salt of a carboxylic acid selected from the group consisting of zinc salts of fatty acids, the zinc salts of hydrocarbyl-substituted salicyclic acids and zinc glyoxylates.

However, none of EP-A-1314774, EP-A-0767237 and EP-A-0761806 are concerned with improving fretting corrosion properties. In this regard, the skilled person would appreciate that fretting corrosion is a very different phenomena from CVJ flaking.

It is highly desirable to be able to offer lubricating grease compositions with advantageous anti-fretting characteristics.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention it has been surprising that specific lubricating grease compositions may be used in order to reduce fretting corrosion.

Accordingly, there is provided in the present invention the use of a lubricating grease composition comprising:

-   -   (A) base oil selected from mineral oil, synthetic oil, or         mixtures thereof;     -   (B) one or more urea compounds; and     -   (C) one or more metal salts of a fatty acid wherein the metal is         selected from the group consisting of aluminium, magnesium,         zinc, calcium and mixtures thereof, in order to reduce fretting         corrosion.

The base oil in the lubricating grease composition may be selected from mineral oil, synthetic oil or mixtures thereof. Synthetic oils are particularly preferred.

The mineral oils that may be conveniently used are the refined residues of lubricating oils obtained by vacuum distillation of atmospheric-pressure residual oils obtained by atmospheric distillation of crude oil, examples of which are paraffin oils, naphthene oils or normal paraffin.

Examples of synthetic oils that may be conveniently used include poly-α-olefins (PAOs), ether oils or ester oils. Base oils of the type manufactured by the hydroisomerisation of wax, such as those sold by the Shell group under the trade designation “XHVI” may also be used.

Poly-α-olefins include oligomers of alkenes such as decene, dodecene or 1-tetradecene, which oligomers comprise oligomer mixtures of di- to hexamers. PAOs may be conveniently selected according to viscosity and degree of polymerisation.

As ether oils, alkyldiphenyl ethers may be conveniently used. Said ethers are the addition reaction products of 1 mol ordinary diphenyl ether and from 1 to 3 mol of α-olefins having from 10 to 22 carbons. The characteristics of α-olefins differ according to the number of carbons and the mole numbers used, but they are generally colourless to transparent liquids, and are themselves known products. Specifically, it is possible to use those disclosed in Japanese Patent Publication 51-44263, Japanese Patent Publication 52-1722 and Japanese Patent Publication 52-24628.

Examples of alkyldiphenyl ether oils which are commercially available, include those available under the trade designations “Moresco Hilube LB-15”, “Moresco Hilube LB-22”, “Moresco Hilube LB-32”, “Moresco Hilube LB-46”, “Moresco Hilube LB-68” and “Moresco Hilube LB-100” from Matsumura Oil Research Corporation.

As ester oils, diester oils, triester oils and tetraester oils may be conveniently used.

The diester oils may be expressed by the general formula (1): R₁OCO(—CH₂—)_(n)COOR₂   (1) wherein R₁ and R₂ denote aliphatic hydrocarbon groups having from 3 to 18 carbon atoms and n is an integer from 3 to 12.

Examples of ester oils that may be conveniently used include di-2-ethylhexyl sebacate, di-2-ethylhexyl azelate, di-2-ethylhexyl adipate, di-n-octyl sebacate, di-n-octyl azelate and di-n-octyl adipate.

The triester oils may be expressed by the general formula (2): R₁—C(—CH₂—COOR₂)₃   (2) wherein R₁ denotes a hydrogen atom or an aliphatic hydrocarbon group having from 1 to 10 carbons and R₂ denotes an aliphatic hydrocarbon group having from 3 to 18 carbon atoms. It is particularly preferred if R₂ is an aliphatic hydrocarbon group having from 3 to 10 carbon atoms.

For example, the triesters may be reaction products of fatty acids and trihydric alcohols such as trimethylolpropane and glycerine.

The tetraester oils may be expressed by the general formula (3): C(—CH₂—COOR₁)₄   (3) wherein R₁ denotes an aliphatic hydrocarbon group having from 3 to 18 carbon atoms. It is particularly preferred if R₁ is an aliphatic hydrocarbon group having from 3 to 10 carbon atoms.

For example, the tetraesters may be reaction products of fatty acids and tetrahydric alcohols such as pentaerythritol.

It is also possible to use mixtures of the above-mentioned mineral oils and synthetic oils as the base oil (A).

Because the kinematic viscosity of the base oil contributes to low-torque performance, it is preferable for the base oil (A) to have a kinematic viscosity in the range of from 10 to 40 mm²/s (40° C.).

The one or more urea compounds (B) in the lubricating grease composition may be conveniently chosen from the urea compounds used as thickening agents in typical lubricating grease compositions.

Preferred urea compounds are diurea compounds, triurea compounds and tetraurea compounds.

The diurea compounds are reaction products of diisocyanates and monoamines which may be aliphatic amines, alicyclic amines and/or aromatic amines.

Examples of the monoamines that may be conveniently used include octylamine, decylamine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, oleylamine, aniline, p-toluidine, cyclohexylamine.

Further, examples of diisocyanates that may be conveniently used include aliphatic diisocyanates, alicyclic diisocyanates and aromatic diisocyanates: for example, 4,4′-diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), naphthalene diisocyanate, p-phenylene diisocyanate, trans-1,4-cyclohexane diisocyanate (CHDI), 1,3-bis-(isocyanatomethyl-benzene), 4,4′-dicyclohexylmethane diisocyanate (H12MDI), 1,3-bis-(isocyanatomethyl)-cyclohexane (H6XDI), hexamethylene diisocyanate (HDI), 3-isocyanatomethyl-3,3,5′-trimethylcyclohexylisocyanate (IPDI), phenylene diisocyanate, m-tetramethylxylene diisocyanate (m-TMXDI) and p-tetramethylxylene diisocyanate (p-TMXDI). In particular, 4-4′-diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), trans-1,4-cyclohexane diisocyanate (CHDI) and 4,4′-dicyclohexylmethane diisocyanate (H12MDI) are preferred.

The triurea compounds may be expressed by the general formula (4):

wherein R₁ and R₂ denote hydrocarbylene groups, and R₃ and R₄ denote hydrocarbyl groups.

These compounds are reaction products of 2 mol aliphatic, alicyclic or aromatic diisocyanate, 1 mol aliphatic, alicyclic or aromatic diamine, 1 mol aliphatic, alicyclic or aromatic amine and 1 mol aliphatic, alicyclic or aromatic alcohol. They are obtained by mixing the aforementioned compounds in base oil so as to give the respective aforementioned proportions, and effecting the reaction. For example, they may be obtained by reacting 2 mol tolylene diisocyanate, 1 mol ethylene diisocyanate, 1 mol octadecylamine and 1 mol octadecyl alcohol in a base oil.

Examples of the aliphatic, alicyclic or aromatic diisocyanates that may be conveniently used include 4,4′-diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), naphthalene diisocyanate, p-phenylene diisocyanate, trans-1,4-cyclohexane diisocyanate (CHDI), 1,3-bis-(isocyanatomethyl-benzene), 4,4′-dicyclohexylmethane diisocyanate (H12MDI), 1,3-bis-(isocyanatomethyl)-cyclohexane (H6XDI), hexamethylene diisocyanate (HDI), 3-isocyanatomethyl-3,3,5′-trimethylcyclohexylisocyanate (IPDI), phenylene diisocyanate, m-tetramethylxylene diisocyanate (m-TMXDI) and p-tetramethylxylene diisocyanate (p-TMXDI). In particular, 4-4′-diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), trans-1,4-cyclohexane diisocyanate (CHDI) and 4,4′-dicyclohexylmethane diisocyanate (H12MDI) are preferred.

Examples of monoamines that may be conveniently used include aliphatic, alicyclic and aromatic monoamines. Aliphatic monoamines are preferably saturated or unsaturated aliphatic amines with from 8 to 24 carbon atoms and may be used in branched or straight-chain forms, but straight-chain forms are particularly preferred.

Octylamine, decylamine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, oleylamine, aniline, p-toluidine, cyclohexylamine are preferred.

Aliphatic, alicyclic or aromatic diamines, aliphatic diamines that may be conveniently used are ethylenediamine, trimethylenediamine, tetramethylenediamine, hexamethylenediamine, octamethylenediamine and decamethylenediamine, alicyclic diamines such as diaminocyclohexane, and aromatic diamines such as phenylenediamine, benzidine, diaminostilbene and tolidine, which are all diamines with from 2 to 12 carbon atoms therein.

Examples of monoalcohols that may be conveniently used are aliphatic, alicyclic or aromatic alcohols branched or straight-chain. Aliphatic alcohols, which are C₈ to C₂₄ saturated or unsaturated aliphatic alcohols may be conveniently used. Straight-chain forms are particularly preferred.

In particular octyl alcohol, decyl alcohol, dodecyl alcohol, tetradecyl alcohol, hexadecyl alcohol, octadecyl alcohol and oleyl alcohol are preferred.

An example of an alicyclic alcohol that may be conveniently used is cyclohexyl alcohol. Examples of aromatic alcohols that may be conveniently used include benzyl alcohol, salicyl alcohol, phenethyl alcohol, cinnamyl alcohol and hydrocinnamyl alcohol.

The tetraurea compounds may be expressed by the general formula (5):

wherein R₁ and R₂ denote hydrocarbylene groups and R₃ denotes a hydrocarbyl group.

These compounds are reaction products of 2 mol aliphatic, alicyclic or aromatic diisocyanate, 1 mol aliphatic, alicyclic or aromatic diamine and 2 mol aliphatic, alicyclic or aromatic amine. They are obtained by mixing the aforementioned compounds in a normal base oil so as to give the respective aforementioned proportions, and effecting the reaction. For example, they may be obtained by reacting 2 mol tolylene diisocyanate, 1 mol ethylenediamine and 2 mol octadecylamine in base oil.

Examples of diisocyanates that may be conveniently used include aliphatic diisocyanates, alicyclic diisocyanates and aromatic diisocyanates: for example, 4,4′-diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), naphthalene diisocyanate, p-phenylene diisocyanate, trans-1,4-cyclohexane diisocyanate (CHDI), 1,3-bis-(isocyanatomethyl-benzene), 4,4′-dicyclohexylmethane diisocyanate (H12MDI), 1,3-bis-(isocyanatomethyl)-cyclohexane (H6XDI), hexamethylene diisocyanate (HDI), 3-isocyanatomethyl-3,3,5′-trimethylcyclohexylisocyanate (IPDI), phenylene diisocyanate, m-tetramethylxylene diisocyanate (m-TMXDI) and p-tetramethylxylene diisocyanate (p-TMXDI). In particular, 4-4′-diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), trans-1,4-cyclohexane diisocyanate (CHDI) and 4,4′-dicyclohexylmethane diisocyanate (H12MDI) are preferred.

For the aliphatic, alicyclic or aromatic diamines, aliphatic diamines such as ethylenediamine, trimethylenediamine, tetramethylenediamine, hexamethylenediamine, octamethylenediamine and decamethylenediamine, alicyclic diamines such as diaminocyclohexane, and aromatic diamines such as phenylenediamine, benzidine, diaminostilbene and tolidine, which are all diamines with from 2 to 12 carbon atoms, may be conveniently used.

For the monoamines, aliphatic, alicyclic and aromatic monoamines may be conveniently used. Branched or straight-chain aliphatic monoamines which are saturated or unsaturated aliphatic amines with from 8 to 24 carbon atoms are preferred. Straight-chain saturated or unsaturated aliphatic amines with from 8 to 24 carbon atoms are particularly preferred.

As an example of an alicyclic monoamine, cyclohexylamine may be cited.

As examples of aromatic monoamines, aniline and p-toluidine may be cited.

The one or more urea compounds (B) are preferably blended in an amount in the range of from 2 to 30% by weight, and more preferably in the range of from 2 to 20% by weight, based on the total weight of the lubricating grease composition. If the amount of said one or more urea compounds (B) is less than 2% by weight, then the effect of the thickening agent may be too small and the consistency may not be that of a grease. If the amount of said one or more urea compounds (B) exceeds 30% by weight, then the grease may become too hard and sufficient lubricating effect may not be obtained.

The one or more metal salts of a fatty acid in the lubricating grease composition are preferably metal salts which are comprised of saturated or unsaturated fatty acids having from 4 to 18 carbon atoms, which may also comprise one or more hydroxyl groups, wherein the metal is selected from the group comprised of aluminium, magnesium, zinc, calcium and mixtures thereof.

Metal salts of a fatty acid wherein the metal is selected from zinc, aluminium and magnesium are preferred. Particularly preferred metal salts of a fatty acid are those wherein the metal is selected from zinc and aluminium.

Fatty acids that may be conveniently used for the metal salts of a fatty acid include: as straight-chain saturated acids, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid and 12-hydroxystearic acid; as branched saturated acids, 4-6-dimethyloctanoic acid, 2-methylundecanoic acid, 2-methyltetradecanoic acid and 2-ethylpentadecanoic acid; as unsaturated acids, 3-octenoic acid, 2-decenoic acid, caproleinic acid, myristoleinic acid, 2-methyl-2-dodecenoic acid, oleic acid, elaidic acid, linolic acid, linolenoic acid and risinolic acid.

Lubricating grease compositions having extremely good anti-fretting properties are obtained by blending preferably in the range of from 0.1 to 25% by weight, more preferably in the range of from 0.5 to 20% by weight, of said one or more metal salts of fatty acid wherein metals selected from the group comprising aluminium, magnesium, zinc, calcium and mixtures thereof, based on the total weight of the lubricating grease composition.

If said one or more metal salts of a fatty acid are present in an amount of less than 0.1% by weight, then the effect of the anti-fretting properties may be inadequate, and if it exceeds 25% by weight, then the effect of the one or more metal salts of a fatty acid may become too powerful and the effect of the anti-fretting properties may diminish.

The lubricating grease composition may contain, as required, additional additives such as anti-oxidants, rust inhibitors, metal corrosion inhibitors, oiliness agents (also known as friction modifiers), anti-wear agents, extreme-pressure additives and solid lubricant additives.

Examples of additives include anti-oxidants such as 2,6-ditertiary-butyl-4-methylphenol, N-phenyl-α-naphthylamine and 2,6-ditertiary-butyl para-cresol, rust inhibitors such as oxidised paraffin, aminoimidazoline, N,N′-trimethylenediamine diolate, sorbitan monoolate, metal sulphonates, alkenyl succinates and derivatives thereof, ester-type rust inhibitors or amine-type rust inhibitors, anti-wear or extreme-pressure additives such as sulphur compounds, for example, olefin sulphide, sulphurised oils and fats, diphenyl disulphide and dibenzyl disulphide, chlorine compounds such as chlorinated diphenyl or chlorinated paraffin, dithiophosphates such as zinc dithiophosphate and molybdenum dithiophosphate, dithiocarbamates such as zinc dithiocarbamate and molybdenum dithiocarbamate, phosphorus compounds such as phosphate esters, for example, tricresylphosphate, phosphite esters, thiophosphate esters and dithiophosphate esters.

The present invention further provides a method of reducing fretting corrosion in devices such as bearings, splines, couplings and leaf springs, said method comprising lubricating said devices with a lubricating grease composition as hereinbefore described.

It is possible to offer by means of the method of the present invention a lubricating grease composition capable of greatly improving anti-fretting properties, and bearings, splines, couplings and leaf springs using said lubricating grease composition.

The present invention is described below with reference to the following Examples, which are not intended to limit the scope of the present invention in any way.

EXAMPLES

The results of experiments on the Examples and the Comparative Examples are shown below.

The diurea compounds used as the thickening agent in the lubricating grease compositions are shown by general formula (6):

and:

-   Aliphatic A is a diurea compound where R is a saturated alkyl group     with 8 carbon atoms; -   Aliphatic B is a diurea compound where R is a saturated alkyl group     with 12 carbon atoms; -   Aliphatic C is a diurea compound where R is a saturated alkyl group     with 18 carbons; -   Aliphatic D is a diurea compound comprised of 50 mol % Aliphatic A     and 50 mol % Aliphatic B; -   Aliphatic E is a diurea compound comprised of 50 mol % Aliphatic A     and 50 mol % Aliphatic C; -   Aliphatic F is a diurea compound which is the reaction product of     tolylene diisocyanate (TDI) and octylamine, an 80:20 mixture of     toluene-2,4-diisocyanate:toluene-2,6- diisocyanate being used for     the tolylene diisocyanate; and -   Aromatic A is the reaction product of p-toluidine and MDI.

The base oils used in the lubricating grease compositions that were tested were:

-   Mineral Oil A: a paraffinic mineral oil with a kinematic viscosity     of 4 mm²/s at 100° C.; -   Mineral Oil B: a paraffinic mineral oil with a kinematic viscosity     of 11 mm²/s at 100° C.; -   Synthetic Oil A: a poly-α-olefin with a kinematic viscosity of 6     mm²/s at 100° C. (available under the trade designation “Hitec-166”     from Ethyl Japan Corporation); -   Synthetic Oil B: an alkyldiphenyl ether with a kinematic viscosity     of 5.6 mm²/s at 100° C. (available under the trade designation     “Moresco Hilube LB-32” from Matsumura Oil Research Corporation); -   Synthetic Oil C: a polyol ester with a kinematic viscosity of 6     mm²/s at 100° C. (available under the trade designation “Kaolube”     from Kao Corporation).

The abbreviations for some of the metal salts of a fatty acid used in the lubricating grease compositions that were tested are shown in the tables as:

-   Mg-St: magnesium stearate -   Ca-St: calcium stearate -   Li-St: lithium stearate -   Ca-12(OH)St: calcium 12-hydroxystearate -   Li-12(OH)St: lithium 12-hydroxystearate -   Zn-St: zinc stearate -   Al-St: aluminium stearate.

The properties representing the headings in the tables were established by the following test methods:

Penetration: JIS K 2220 5, 3

Dropping point: JIS K2220 5, 4

For anti-fretting, fretting abrasion tests were carried out in accordance with ASTM D4170.

Anti-fretting, room temperature, shows the results of fretting abrasion experiments for 22 hours at 25° C., while anti-fretting, low temperature, shows the results of fretting abrasion experiments for 22 hours at −30° C.

With regard to the amount of fretting abrasion, results are graded as follows:

-   -   Θ shows that the amount of fretting abrasion is under 1.5         mg—i.e. anti-fretting abrasion inhibition effect was extremely         large;     -   λ shows that the amount of fretting abrasion is in the range of         from 1.5 to 5.0 mg—i.e. anti-fretting abrasion inhibition effect         was large;     -   Δ shows that the amount of fretting abrasion is in the range of         from 5.0 to 15.0 mg—i.e. there was a small anti-fretting         abrasion inhibition effect;     -   X shows that the amount of fretting abrasion is above 15.0         mg—i.e. anti-fretting abrasion inhibition effect was poor.

Examples of 1 to 5

Lubricating grease compositions were obtained by mixing and heating the thickening agents, base oils and additives shown in Table 1 in the proportions shown in Table 1.

The results of measuring the penetration, dropping point (°C.) and anti-fretting (room temperature) of the lubricating grease compositions obtained are shown in Table 1. TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Thickening Diurea 10 10 10 10 10 agent Compound: Aliphatic A Base oil Mineral Oil A 89 89 89 89 89 Additives Mg-St 1 Ca-St 1 Ca-12(OH)St 1 Zn-St 1 Al-St 1 Results Penetration 285 282 284 283 281 (dmm) Dropping >250 >250 >250 >250 >250 point ° C. Anti-fretting ◯ Δ Δ Θ Θ grade, room temp. Anti-fretting 3.9 8.3 13.2 0.2 0.3 (mg), room temp.

With regard to the influence of the metals on the urea greases and stearate metal salts:

Ca-St: There was some fretting abrasion inhibition effect.

Mg-St: The fretting abrasion inhibition effect was large.

Zn-St and Al-St: The fretting abrasion inhibition effect was extremely large.

As a result it was clear that, among the metal salts of a fatty acid, salts wherein the metal was Zn or Al had a particularly superior effect.

Comparative Examples 1 to 6

Similar experiments were carried out by varying the base oil for cases where a single diurea compound was used as the thickening agent. The results are shown in Table 2. TABLE 2 Comp. Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Thickening Diurea agent Compound: Aliphatic A 10 10 10 10 Aliphatic B 30 Aliphatic C 8 Base oil Mineral Oil A 90 70 92 Synthetic oil A 90 Synthetic oil B 90 Synthetic oil C 90 Headings Penetration 278 280 280 283 294 275 (dmm) Dropping >250 >250 >250 >250 185 >250 Point ° C. Anti-fretting X X X X X X grade, room temp. Anti-fretting 19.3 16.1 34.1 29.4 26.4 17.9 result (mg), room temp.

In these results, no anti-fretting characteristic was observed with only a urea compound blended with the base oil.

Comparative Examples 7 and 8

Similar experiments were carried out for the cases where lithium stearate or lithiun 12-hydroxystearate was added, under heat, to the diurea compound. The results are shown in Table 3. TABLE 3 Comparative Comparative Example 7 Example 8 Thickening Diurea compound: Agent Aliphatic A 10 10 Base oil Mineral Oil A 89 89 Additives Li-St 1 Li-12(OH)St 1 Results Penetration (dmm) 281 286 Dropping point ° C. >250 >250 Anti-fretting grade X X Room temperature Anti-fretting result 21.3 20.6 (mg), room temp.

Virtually no anti-fretting characteristic was observed even when a lithium salt of a fatty acid was added to the urea grease.

Examples 6 to 13

Similar experiments were carried out by varying the base oil. The results are shown in Table 4. TABLE 4 Ex. Ex. Ex. Ex. Ex. 6 Ex. 7 Ex. 8 Ex. 9 10 11 12 13 Thickening Diurea compound: Agent Aliphatic A 10 10 10 10 10 10 10 10 Base oil Mineral Oil B 89 89 Synthetic oil A 89 89 Synthetic oil B 89 89 Synthetic oil C 89 89 Additives Zn-St 1 1 1 1 Al-St 1 1 1 1 Results Penetration (dmm) 270 285 284 288 270 288 286 289 Dropping point ° C. >250 >250 >250 >250 >250 >250 >250 >250 Anti-fretting grade, Θ Θ Θ Θ Θ Θ Θ Θ room temperature Anti-fretting result 0.7 0.2 1.1 0.9 0.9 0.3 1.3 1.2 (mg), room temperature

According to these results, when the diurea compound and zinc stearate or aluminium stearate are blended into the base oil, both have an extremely large anti-fretting abrasion inhibition effect, and substantially no influence on the anti-fretting abrasion inhibition effect according to type of base oil was observed.

Examples of Embodiment 14 to 17

Similar experiments were carried out by varying the amount of thickening agent added. The results are shown in Table 5. TABLE 5 Exam- Exam- ple ple Example Example 14 15 16 17 Thickening Diurea Agent compound: Aliphatic A 15 15 Aliphatic C 10 10 Base oil Mineral Oil A 84 84 89 89 Additives Zn-St 1 1 Al-St 1 1 Headings Penetration 257 256 250 253 (dmm) Dropping >250 >250 >250 >250 point ° C. Anti- Θ Θ Θ Θ fretting grade, room temp. Anti- 0.2 0.3 0.3 0.6 fretting result (mg), room temp.

According to these results, the anti-fretting abrasion inhibition effect was extremely large even when the grease consistency was hard.

Examples of Embodiment 18 to 29

Similar experiments were carried out by varying the type of thickening agent, and its effect was considered.

The results are shown in Tables 6 and 7. TABLE 6 Ex. Ex. Ex. Ex. Ex. Ex. 18 19 20 21 22 23 Thickening Diurea Agent compound: Aliphatic B 30 30 Aliphatic C 8 8 Aliphatic D 12 12 Aliphatic E Aliphatic F Aromatic A Base oil Mineral Oil A 69 69 91 91 87 87 Additives Zn-St 1 1 1 Al-St 1 1 1 Results Penetration 298 300 288 290 290 293 (dmm) Dropping >250 >250 >250 >250 >250 >250 point ° C. Anti- Θ Θ Θ Θ Θ Θ fretting grade, room temperature Anti- 0.2 0.2 0.4 0.6 0.3 0.3 fretting result (mg), room temp.

TABLE 7 Ex. Ex. Ex. Ex. Ex. Ex. 24 25 26 27 28 29 Thickening Diurea agent compound: Aliphatic B Aliphatic C Aliphatic D Aliphatic E 9 9 Aliphatic F 13 13 Aromatic A 22 22 Base oil Mineral Oil A 90 90 86 86 77 77 Additives Zn-St 1 1 1 Al-St 1 1 1 Results Penetration 297 300 288 291 299 301 (dmm) Dropping >250 >250 >250 >250 >250 >250 point ° C. Anti- Θ Θ Θ Θ Θ Θ fretting grade, room temperature Anti- 0.2 0.3 0.5 0.5 0.4 0.4 fretting result (mg), room temp.

The results did not change even when the type of thickening agent constituted by the urea compound was varied.

Example of 30

A lubricating grease composition was obtained by mixing, at room temperature, 7% by weight of Aliphatic A as the diurea compound and 1% by weight of aluminium stearate with 92% by weight of Mineral Oil A.

The penetration of this lubricating grease composition was 276 and the dropping point was above 250 (°C.). The anti-fretting abrasion inhibition effect at room temperature was extremely large (0.3 mg).

Examples 31 to 35

The effect of varying the amount of aluminium stearate added was investigated. The results are shown in Table 8. TABLE 8 Ex. Ex. Ex. Ex. Ex. 31 32 33 34 35 Thickening Diurea compound: Agent Aliphatic A 7 7 6.5 6.3 5.6 Base oil Mineral Oil A 92.9 92.5 88.5 83.7 74.4 Additives Al-St 0.1 0.5 5 10 20 Results Penetration 278 278 270 261 235 (dmm) Dropping point >250 >250 247 244 242 ° C. Anti-fretting ◯ ◯ ◯ Δ Δ grade, room temperature Anti-fretting 4.8 3.2 4.7 13.5 14.7 result (mg), room temperature

It was evident that the amount of aluminium stearate added should preferably be in the range of from 0.1 to 20% by weight and that its effect is particularly large when present in the range of from 0.1 to 5% by weight.

Examples 36 to 39

The effect of varying the fatty acid comprised in the fatty acid metal salt was investigated. The results are shown in Table 9. TABLE 9 Exam- Exam- ple ple Example Example 36 37 38 39 Thickening Diurea Agent compound: Aliphatic A 7 7 7 7 Base oil Mineral Oil A 92 92 92 92 Additives Zn laurate, 1 Saturated Zn myristate 1 Saturated Zn oleate 1 Unsaturated Al oleate, 1 Unsaturated Results Penetration 282 284 281 283 (dmm) Dropping >250 >250 >250 >250 point ° C. Anti- Θ Θ Θ Θ fretting grade, room temperature Anti- 0.1 1.4 0.1 0.1 fretting result (mg), room temp.

From these results, it was evident that the effect was large irrespective of whether the fatty acid comprised in the fatty acid metal salt was a saturated fatty acid or an unsaturated fatty acid.

Examples 40 to 42

Fretting abrasion tests were carried out for 22 hours at −30° C. when using Synthetic Oil A as the base oil.

The results are shown in Table 10. TABLE 10 Example Example Example 40 41 42 Thickening Diurea compound: agent Aliphatic A 7 7 7 Base oil Synthetic Oil A 92 92 92 Additives Mg-St 1 Zn-St 1 Al-St 1 Headings Penetration (dmm) 285 288 286 Dropping point ° C. >250 >250 >250 Anti-fretting ◯ ◯ Θ grade, low temperature Anti-fretting 3.8 1.6 0.5 result (mg), low temperature

An improvement in the anti-fretting characteristics was observed even at low temperature.

Examples 43 to 44

The effect of using a tetraurea compound and a triurea urethane compound in place of a diurea compound was investigated.

For the tetraurea compound, a uniform solution was made by adding 7.49 g of tolylene diisocyanate to 100 g of base oil, and heating to 50° C. To this solution were added 11.75 g of oleylamine and 1.29 g of ethylenediamine dissolved in 80 g of base oil. When the mixture was agitated a gel-like substance was immediately produced.

While continuing the agitation, the temperature was increased to 150° C. and, after that temperature was maintained for 30 minutes, 2.0 g of metallic salt was added and the mixture was held like this for 15 minutes before being cooled. A grease was then prepared using a three-roll mill. A grease composition containing 10% by weight of a tetraurea compound was thus obtained.

For the triurea compound, a uniform solution was made by adding 9.20 g of tolylene diisocyanate and 7.14 g of stearyl alcohol to 100 g of base oil, and heating to 50° C.

Next, 4.05 g of tallow amine and 1.56 g of ethylenediamine dissolved in 77 g of base oil were added to this solution which was kept at 90 to 150° C. and this was allowed to react with the unreacted isocyanate. 2.0 g of metal salt was then added and the mixture was held for 15 minutes like this before being cooled. A grease was then prepared using a three-roll mill. A grease composition containing 11% by weight of a triurea urethane compound was thus obtained. TABLE 11 Example 43 Example 44 Thickening Tetraurea compound 10 agent Triurea urethane 11 compound Base oil Mineral Oil A 89 88 Additives Al-St 1 1 Results Penetration (dmm) 271 293 Dropping point ° C. >250 >250 Anti-fretting grade, Θ Θ room temperature Anti-fretting result 0.7 0.9 (mg), room temp.

Even when the urea compound was varied, it was possible to improve the anti-fretting characteristics substantially. 

1. Use of a lubricating grease composition comprising: (A) base oil selected from mineral oil, synthetic oil, or mixtures thereof, (B) one or more urea compounds, and (C) one or more metal salts of a fatty acid wherein the metal is selected from the group consisting of aluminium, magnesium, zinc, calcium and mixtures thereof, in order to reduce fretting corrosion.
 2. Use according to claim 1, wherein the lubricating grease composition comprises an amount in the range of from 2 to 30% by weight of the one or more urea compounds (B), based on the total weight of the lubricating grease composition.
 3. Use according to claim 1, wherein the one or more urea compounds (B) are diurea compounds.
 4. Use according to claim 1, wherein the one or urea compounds (B) are triurea compounds expressed by the general formula (4):

wherein R₁ and R₂ denote hydrocarbylene groups and R₃ and R₄ denote hydrocarbyl groups.
 5. Use according to claim 1, wherein the one or more urea compounds (B) are tetraurea compounds expressed by the general formula (5):

wherein R₁ and R₂ denote hydrocarbylene groups and R₃ denotes a hydrocarbyl group.
 6. Use according to claim 1, wherein the lubricating grease composition comprises an amount in the range of from 0.1 to 25% by weight of the one or more metal salts of a fatty acid (C), based on the total weight of the lubricating grease composition.
 7. Use according to claim 1, wherein the one or more metal salts of a fatty acid (C) are metal salts of a saturated or unsaturated fatty acid having from 4 to 18 carbon atoms, which may also comprise one or more hydroxyl groups, wherein the metal is selected from the group comprised of aluminium, magnesium, zinc and calcium and mixtures thereof.
 8. Use according to claim 1, wherein the base oil (A) is a poly-α-olefin.
 9. Use according to claim 1, wherein the base oil (A) is an ether oil.
 10. Use according to claim 1, wherein the base oil (A) is an ester oil.
 11. Method of reducing fretting corrosion in bearings, splines, couplings and leaf springs, said method comprising lubricating said bearings, splines, couplings and leaf springs with a lubricating grease composition as described in claim
 1. 12. Use according to claim 2, wherein the lubricating grease composition comprises an amount in the range of from 0.1 to 25% by weight of the one or more metal salts of a fatty acid (C), based on the total weight of the lubricating grease composition.
 13. Use according to claim 3, wherein the lubricating grease composition comprises an amount in the range of from 0.1 to 25% by weight of the one or more metal salts of a fatty acid (C), based on the total weight of the lubricating grease composition.
 14. Use according to claim 4, wherein the lubricating grease composition comprises an amount in the range of from 0.1 to 25% by weight of the one or more metal salts of a fatty acid (C), based on the total weight of the lubricating grease composition.
 15. Use according to claim 5, wherein the lubricating grease composition comprises an amount in the range of from 0.1 to 25% by weight of the one or more metal salts of a fatty acid (C), based on the total weight of the lubricating grease composition.
 16. Use according to claim 2, wherein the one or more metal salts of a fatty acid (C) are metal salts of a saturated or unsaturated fatty acid having from 4 to 18 carbon atoms, which may also comprise one or more hydroxyl groups, wherein the metal is selected from the group comprised of aluminium, magnesium, zinc and calcium and mixtures thereof.
 17. Use according to claim 3, wherein the one or more metal salts of a fatty acid (C) are metal salts of a saturated or unsaturated fatty acid having from 4 to 18 carbon atoms, which may also comprise one or more hydroxyl groups, wherein the metal is selected from the group comprised of aluminium, magnesium, zinc and calcium and mixtures thereof.
 18. Use according to claim 4, wherein the one or more metal salts of a fatty acid (C) are metal salts of a saturated or unsaturated fatty acid having from 4 to 18 carbon atoms, which may also comprise one or more hydroxyl groups, wherein the metal is selected from the group comprised of aluminium, magnesium, zinc and calcium and mixtures thereof.
 19. Use according to claim 5, wherein the one or more metal salts of a fatty acid (C) are metal salts of a saturated or unsaturated fatty acid having from 4 to 18 carbon atoms, which may also comprise one or more hydroxyl groups, wherein the metal is selected from the group comprised of aluminium, magnesium, zinc and calcium and mixtures thereof.
 20. Use according to claim 6, wherein the one or more metal salts of a fatty acid (C) are metal salts of a saturated or unsaturated fatty acid having from 4 to 18 carbon atoms, which may also comprise one or more hydroxyl groups, wherein the metal is selected from the group comprised of aluminium, magnesium, zinc and calcium and mixtures thereof. 